Wednesday, April 22, 2009

Geology Will Be Central To India's Climate Change Response

A friend returned from Australia with stories of water rationing in Melbourne and Adelaide. Can't water lawns and wash cars. That would invite fines from the city. Coincidentally, national geographic magazine has a feature on Australia's big dry, a prolonged drought that has decimated farming communities in the Murray Darling basin and forced farmers to sell century old farms and move to cities in search of work.

As always I want to steer the conversation to what is happening in India. A recent regional finer grained climate model from researchers at Purdue University confirms what global climate models have been telling us for some time. That monsoon patterns will change both in the timing of the advent of rains and in the amount of precipitation. The map below shows the across-country expected changes in both these parameters.

Source: Purdue

The basic take away lessons from these studies are that: 1) the country will get hotter 2) rainfall pattern will be more unpredictable 3) rains will be concentrated in shorter more intense bursts 4) periods of drought will last longer 5) overall, regions which experience less rainfall can expect even less rainfall, those that experience a lot of rain can expect little change or an increase in rain.

I turn again to the National Water Mission, one of the eight focus areas in the National Action Plan for Climate Change (15 mb) It does recognize that water availability and rainfall will vary region by region and proposes a host of measures in its draft report that includes enhancement and better management of groundwater resources as well as surface water resources.

That is fine talk but will the resource allocation and effort match the current pattern of water use? Himanshu Thakkar in a detailed critique of the National Action Plan For Climate Change is pessimistic about any fundamental changes taking place in the way the government thinks about water resources. Yet, today over two thirds of arable lands in India are irrigated by groundwater and over 85% of rural water supply and about 50% of urban and industrial water supply comes from groundwater sources. Historically though it is surface water that has received more attention and funding. Our government planners have always been obsessed with mega infra-structure water projects.

Despite hundreds of kilometers of canals, surface water irrigation helps less than 15% of Indian farmlands. The majority rely on direct rain and groundwater supported by about 20 million irrigation wells. It is the small landholders and marginal farmers who benefit most from groundwater. From 1970 to 1995 marginal farms increased their groundwater irrigated areas by 400 percent as compared with just 1 percent increase for large farms, which seem to rely more on canal irrigation.

Looking at the above numbers, at how the water resources pie is divvied up by users, it is groundwater that should be the priority of the National Water Mission. Its not just the lessons from the past regarding the inadequacy of big dams /canals that should guide a shift in focus, but also the realization that climate change will render these systems even more ineffective in the future. Shorter more intense bursts of rain would mean more vigorous surface flow and soil erosion. This would mean increased rates of siltation of canals and dams and a rapid decrease in storage capacity. And a hotter India would mean increased evaporative losses from larger surface reservoirs.

Storing water underground minimizes this loss of water through decreased capacity and evaporation. But a groundwater based strategy faces its own challenges. I am placing below a map of aquifers of India. Compare the spatial distribution of aquifer types with the climate model above.

Source: WHYMAP

Over large tracts of the country, areas that are projected to receive less rainfall in the future are underlain by hydrogeologically complex aquifers!

These are the Precambrian shield areas of south and central India and the Deccan volcanics of central India. In alluvial aquifers which underlie the Indo-Gangetic plains water is stored between sediment grains. There is not a whole lot of spatial variability in water storage properties and although the depth to water table can vary, it is uniform and predictable over large areas. The situation changes in hard rock terrains. Water in these types of crystalline rocks is stored and flows along very restricted zones of permeability. These can be tricky to map. Aquifers are spatially heterogeneous and compartmentalized. Shorter bursts of rain would mean greater surface flow and less seepage underground. That would mean geo-engineering solutions to enhance recharge through careful assessment of recharge zones and use of the 11 million or so dug wells that access aquifers in these hard rock terrains.

If groundwater is to take center stage in our adaptation to climate change geological knowledge will have to play an increasingly important role in how this resource is managed and exploited.

So far aquifer "management" in the few instances it is actually practiced in this country is largely driven by heuristics. But with climate changing and conditions becoming more unpredictable, "this is the way we have done it since our great grandfathers time" may not produce the best results. A more successful approach would be one which uses a more rigorous quantitative understanding of the groundwater systems.

What is the lateral extent and storage capacity of the underlying aquifer? How much water can be sustainably withdrawn from aquifers with particular physical properties? Will certain types of aquifers support certain crop types? We need to improve and enlarge the science programs studying groundwater. Geology comes into the picture in a big way, not just to find groundwater but to manage it as well. That means larger and denser monitoring networks and mathematically inclined geologists to make sense of the incoming data. Geo-engineering solutions to enhance recharge and storage need to be put in place. The increasingly sophisticated understanding of the groundwater systems will have to be explained to the farmers. For that a gentler more transparent interface between geologists and the groundwater user community needs to evolve.

I am not saying anything terribly original here, but scientific management of groundwater is the most economical and environmentally least destructive solution for providing water security to a majority of our farmers.

Now, how do you make the National Water Mission listen?

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